Albert Barnes Commentary 1 Chronicles 26:18

"For Parbar westward, four at the causeway, and two at Parbar." — 1 Chronicles 26:18 (ASV)

Here, "Parbar" must refer to the space between the western wall of the temple building and the wall of the court, which would be a kind of precinct or outer area of the temple (see the note on 2 Kings 23:11). Two gates were in this area; two guards were stationed at one, while four guards were at the Shallecheth Gate, which led to the causeway.

Throughout this account, the temple is described as if it already existed, even though it had not yet been built. We must therefore suppose that David formed the entire plan for the temple, establishing the stations and numbers for the gatekeepers, though it was left for Solomon to carry out his instructions.